At the written maths finals in my country there’s first a timebox where the teacher goes through all tasks to make sure that everyone understands what is asked. During that portion the headmaster is present and students are allowed to ask questions. After that the headmaster leaves and nobody is allowed to talk any more.

So the teacher shows us this one task, and it’s a 3D geometry task. I look through it and notice that there’s one angle missing. There’s an infinite number of correct solutions with the given requirements. So I raise my hand and ask about that.

My teacher looks straight past me at the back wall of the classroom, completely stone faced and says “I am sure that the requirements are complete. They cannot be incomplete.” I hold my tongue.

As soon as the headmaster leaves, my teacher all but runs up to my desk and asks me what he missed.

Turns out, I was right and he just put a random number on the chalkboard to be used as the missed requirement.

If he had admitted in front of the headmaster that the requirements were incomplete, then the whole maths finals would have to be postponed and redone.